At least 24 people -- mostly civilians -- were killed and 105 others were wounded when a bomb went off at a compressed natural gas station Tuesday, officials said.

Tahir Hussain, commissioner of Faisalabad -- where the blast occurred -- called it an act of terrorism.

Ihsanullah Ihsan, spokesman for the Pakistani Taliban, told CNN the target was the regional office of Pakistan's top spy agency, the ISI.

The intelligence agency building experienced no major damage, said Naseem Sadiq, a senior government official in Faisalabad.

Among the dead were an intelligence officer and a schoolteacher, Sadiq said.

Some people were trapped under the rubble but rescuers managed to get them out, officials said.

A large crater at the blast site suggested the explosion was caused by a device planted at the pump, said Hussain. When it went off, it triggered a second explosion at the gas station, he said.

Ihsan said the ISI had killed many Taliban fighters over the years and had handed over some to the United States in return for money. He warned that his group will continue to target the ISI in revenge.

Pakistan has the highest number of vehicles running on compressed natural gas (CNG) as well as the most refueling stations in the world, according to December 2009 figures from the International Association for Natural Gas Vehicles.

The New Zealand-based trade group placed the number of CNG stations in Pakistan at 3,068.